A lot of people are wondering why Nokia didn't choose to go with Android. How can Nokia differentiate themselves when Android is a lot more open and free than Windows Phone 7? As usual, the key to this is in the details. If you read the announcements carefully, you'll see that Microsoft offered Nokia something Google most likely didn't. Update: What a surprise. Elop just confirmed Nokia has a special deal with Microsoft. Whereas HTC, Samsung, and so on are not allowed to customise WP7 - Nokia is, further confirming my theory.

Yes, this deal is much better for Microsoft than for Nokia, just as the deals the OP listed.
Soon Samsung et al are going to go to their sales rep and tell him "wtf dude, why do Nokia get this special treatment? Why arent we allowed to do what they're doing? Get your shit together or we'll move to something else."
After this one of two things will happen. MS will either let all Win7 OEM's do what Nokia does (contracts arent forever, ay know) or the other OEM's will jump ship for something else.
Guess what's Microsoft's preferred option and guess how that will work out for Nokia...